This invention relates generally to radio frequency circuits and more particularly to amplifier circuits.
As is known in the art, distributed amplifiers are used to amplify broadband radio frequency signals. In general, a distributed amplifier includes an input transmission line having a first end coupled to an input terminal of the amplifier, which is used to successfully couple input electrodes of a plurality of transistors to such input terminal. The distributed amplifier also includes an output transmission line coupled to an output terminal of the amplifier, which is used to successfully couple output electrodes of the transistors to the output terminal. A signal fed to the input terminal propagates along signal paths provided through each one of said plurality of transistors and such output signals from the transistors are added in-phase at the output terminal to provide a composite output signal. The inherent reactance between the input electrode and the reference electrode of each transistor is taken into consideration when designing the input transmission line. A broadband network is provided by incorporating such inherent reactance into the input transmission line. Similarly, inherent reactance between the output electrode of each transistor and the reference electrode is also taken into consideration when designing the output transmission line to provide a broadband output network. Such arrangement enables distributed amplifiers to have very broad operating bandwidths.
It is also known in the art that phased array antennas include a plurality of individual radiating elements. Such elements are typically independently controlled to radiate an electromagnetic signal having a selected phase relationship to the other ones of the electromagnetic signals to provide a composite radiation pattern.
One technique for providing desired phase control of the individual radiating elements uses a transceiver circuit which include separate transmit amplifier and receive amplifiers which are fed respective transmit and receive signal through a common phase shifter. It is also known that it is desired to fabricate such circuits as monolithic microwave integrated circuits. Moreover, it would be preferrable to provide such elements on a single monolithic integrated circuit. It would be desirable therefore to eliminate one of the transmit and receive amplifiers. One technique for achieving this would be to simply provide the amplifier in a common path of the transceiver element and thus steer the radio frequency signals via switches operative during transmit and receive through this common path and thus through the amplifier. One problem with this technique, however, is that it requires four RF switches to provide the common steering path. Thus, again increasing the number of circuit elements in the transceiver. Moreover, the switches also increase the insertion loss and noise figure and decrease the gain, output power and efficiency of the transceiver.
Furthermore, in a transceiver, the receive amplifier is generally optimized for low noise operation, whereas the transmit amplifier is generally optimized for high power operation. Therefore, it would be desirable to provide an amplifier which can be used during both transmit and receive and which also obviates the need for switching circuits. Furthermore, it would be more desirable to provide an amplifier which can be optimized both for low noise operation and high power performance.